New catalyst to remove nitrites from drinking water

10:46 AM, 28th November 2013

Researchers at Rice University’s Catalysis and Nanomaterials Laboratory have found that gold and palladium nanoparticles can rapidly break down nitrites.

HOUSTON, US: Nitrites are common and harmful contaminant often found in both groundwater and surface water and cause health hazard. Researchers at Rice University have found a new catalyst that can rapidly break down nitrites that often results from overuse of agricultural fertilizers.

The Environmental Protection Agency places strict limits on the amount of nitrates and nitrites in drinking water. While it’s possible to remove nitrates and nitrites from water with filters and resins, the process can be prohibitively expensive.

“This is a big problem, particularly for agricultural communities, and there aren’t really any good options for dealing with it. Our group has studied engineered gold and palladium nanocatalysts for several years. We’ve tested these against chlorinated solvents for almost a decade, and in looking for other potential uses for these we stumbled onto some studies about palladium catalysts being used to treat nitrates and nitrites; so we decided to do a comparison,” said Michael Wong, Professor, Rice University.

Catalysts are the matchmakers of the molecular world: They cause other compounds to react with one another, often by bringing them into close proximity, but the catalysts are not consumed by the reaction.

Over the past decade, Wong’s team has found these gold-palladium composites have faster reaction times for breaking down chlorinated pollutants than do any other known catalysts.

“There’s no chlorine in these compounds, so the chemistry is completely different. It’s not yet clear how the gold and palladium work together to boost the reaction time in nitrites and why reaction efficiency spiked when the nanoparticles had about 80 per cent palladium coverage. We have several hypotheses we are testing out now,” said Wong.

According to Wong, the gold-palladium nanocatalysts with the optimal formulation were about 15 times more efficient at breaking down nitrites than were pure palladium nanocatalysts, and about seven and half times more efficient than catalysts made of palladium and aluminum oxide.

Wong said he can envision using the gold-palladium catalysts in a small filtration unit that could be attached to a water tap, but only if the team finds a similarly efficient catalyst for breaking down nitrates, which are even more abundant pollutants than nitrites.

“Nitrites form wherever you have nitrates, which are really the root of the problem. We’re actively studying a number of candidates for degrading nitrates now, and we have some positive leads,” said Wong.